Several studies have shown a high incidence of infertile ova present in the uterus of pregnant bonnethead sharks captured along the central Gulf coast of Florida.1,2 The current study was undertaken to determine if the observed infertility was due to endocrinologic changes in either the mature males or mature females and to determine if the infertility could be correlated with elevated serum or tissue concentrations of organochlorine environmental contaminants. To accomplish this, serum and tissues were collected from sharks from three different areas. These areas were Tampa Bay (a highly contaminated area), Florida Bay in the Florida Keys (an area of very low organochlorine contamination), and Apalachicola Bay in the Florida Panhandle (an area of intermediate organochlorine contamination). Differences were found in serum concentrations of reproductive steroid hormones, sites of hormone production, sperm counts and sperm viability, concentrations of various organochlorines, growth and reproductive parameters, and resultant population intrinsic rates of increase. Estradiol concentrations in mature females from Tampa Bay were found to be one-half the concentrations found in the Florida Bay (control) females. There were also significant differences in serum concentrations of estradiol and testosterone from immature females (Tampa Bay < Florida Bay). It is likely that these differences in hormone concentrations are caused by the presence of endocrine-disrupting organochlorine compounds present in the marine environment inhabited by these sharks.
1. Manire CA, LEL Rasmussen, DL Hess, RE Hueter. 1995. Serum steroid hormones and the reproductive cycle of the female bonnethead shark, Sphyrna tiburo. Gen. Comp. Endocrinol. 97:366-376.
2. Parsons GR. 1993. Geographic variation in reproduction between two populations of the bonnethead shark, Sphyrna tiburo. Exp. Biol. Fishes 38:25-35.